The instant invention relates generally to the installation of cables and the like in elongated ducts and conduits, usually underground, and more particularly to a novel tensile tape and clamping device therefor for facilitating such installations.
The present conventional procedure for installing cables and the like in elongated conduits, particularly underground conduits, comprises a multistep method wherein several preliminary lines of gradually increased size and strength are successively pulled through the conduit before the final cable can be installed. First a measuring tape is attached to an air plug and the plug and the tape are blown through the conduit using a compressed air stream. After the length of the conduit has been determined with the measuring tape, and with the tape still in the conduit, a lightweight rope is attached to an end of the tape and is pulled through the conduit. After the rope has been pulled through the conduit, the rope is used to pull a winch line through the conduit in a similar manner and the winch line in turn is used to pull the desired cable through the conduit. These sequential steps are necessary because the measuring tape and rope do not per se possess sufficient tensile strength to pull the heavy cable through the conduit.
Obviously, substantial savings of time and expense could be realized by the elimination of one or more of the above steps from cable installation operations. In particular, it is obvious that by using a measuring tape having a sufficiently high tensile strength, it is possible to use the tape to pull the winch line through the conduit and in some cases, to pull the cable itself through, and thereby eliminate the use of the lightweight rope and the winch line as well. In order to do this, it is essential that the measuring tape have a high tensile strength. However, in order to "blow" the measuring tape through the conduit, the tape must be of comparatively lightweight and must be capable of passing through the conduit with only minimal frictional resistance. Therefore, it is obvious that such a simplified method is only possible using specially coated tapes having extremely high strength-to-weight ratios.
While several types of high strength synthetic fiber tapes have been heretofore available, including tapes comprising KEVLAR (Dupont TM), E-glass and graphite fibers, they have not heretofore been effectively usable in measuring and pull tape applications for a number of reasons. First of all, the known tapes of this type have a tendancy to rub or abrade against the inner surfaces of conduits creating excessive frictional tension, thus making it difficult both to effectively "blow" the tapes through the conduits as aforedescribed, and also to pull them therethrough in subsequent operations. In addition, while these high-strength fibrous tapes have sufficiently high tensile strengths for this type of application, the fibers in these tapes are extremely frangible and hence have a tendancy to fracture if clamped too tightly or if bent sharply, knotted etc. In fact, it has been found that excess clamping or bending of such tapes results in reductions of as much as 60 percent or more in the tensile strengths of the tapes, causing the tapes to fail in their specified functions. As a result, while lightweight tapes of adequate tensile strengths to pull winch lines or lightweight cables through conduits have heretofore been available, the use thereof in this manner has been limited by the unavailability of effective clamping devices for effecting a connection to an end of the tape.
As above stated, a further disadvantage of the heretofore available high-strength, lightweight tapes in cable installation applications has been the excessive frictional resistance created when the tapes rub or abrade against the inner surfaces of conduits. This has limited the effectiveness of the above described air blowing techniques in conduits, particularly in those of substantial lengths, as well as the subsequent pulling operations.
The instant invention overcomes these and other disadvantages by providing a fibrous tape of the type hereinabove described having an antifriction, flexible plastic casing thereon which substantially reduces the resistance created by frictional contact with the inner conduit surfaces, and by providing an effective device for clamping the tape which doesn't cause substantial damage to the fibers therein, so that the tape retains substantially all of its tensile strength. The clamping device of the instant invention is effective for securely clamping fibrous tapes and the like without causing sharp or severe bends therein so that tension is evenly distributed along the tape as it passes through the device without applying damaging crushing forces to the fibers.
In particular, the device of the instant invention comprises an elongated preferably cylindrical body portion preferably having a concave arcuate surface on an end thereof, a first plug half having a first convex arcuate surface thereon which is complimentary to the concave body portion arcuate surface and a first mating surface which is oppositely directed from the first convex arcuate surface, and a second plug half having a second mating surface thereon which is directed toward the first mating surface, and a second convex arcuate surface which is oppositely directed from the second mating surface. Means are provided which laterally retain the first and second mating surfaces in generally mated alignment and simultaneously retain the second plug half proximal to the body portion with the first plug half interposed therebetween and with the first plug half and the body portion arcuate surfaces in generally complimentary relation. A stranded fibrous tensile tape or the like is clamped in the device by positioning the terminal portion of the tape between the opposed mating surfaces of the halves and extending the adjacent portion of the tape along the outer arcuate surface of the second plug half, between the complimentary body portion and second plug half arcuate surfaces and generally away from the body portion in a direction which is generally perpendicular to the opposed mating surfaces. Tensile stresses applied along the tape cause the two plug halves, particularly the mating surfaces thereof, to be urged or drawn together which causes clamping pressure to be applied to the tape between the mating surfaces and also causes pressurized engagement of the tape with the arcuate surfaces of the two plug halves. In one embodiment of the invention, the tape is further retained in the device through the application of even clamping pressures between the complimentary plug and body portion arcuate surfaces. In any case, however, the tape is retained in positive engagement with the various surfaces of the plug halves. By extending the tape along gradual arcuate surfaces, the clamping of the tape is effected without sharp bending thereof and without the application of sharp localized pressure thereto so that damage to the fibers in the tape is avoided. Consequently, the tape retains substantially all of its tensile strength when clamped in the device of the instant invention.
Accordingly, it is an object of the instant invention to provide a device for facilitating the installation of elongated cables and the like in conduits.
Another object of the instant invention is to provide a device for clamping synthetic fibrous tape without causing substantial weakening thereof.
Another object of the instant invention is to provide an effective antifriction fibrous tape for the installation of cables and the like in conduits.
Other objects, features and advantages of the invention shall become apparent as the description thereof proceeds when considered in connection with the accompanying illustrative drawings.